When you delete a file, you remove its inode.. an inode is a special piece of "metadata" that every file/directory must have.

It is essentially the glue that holds the file together, physically a file is split up into blocks or chunks and can be anywhere on the filesystem.. without the inode you'll have no idea where the actual data is, and finding it is improbable.

As jggimi said, this is often asked on the mailing lists.. and the answer is always the same.. make backups, and be careful what you delete.